Nitrite: Review of existing and new physiological data in ruminants

Nitrite is regulated as an undesirable substance in animal feed. “Products and by-products from sugar beet and sugarcane” are currently exempted from maximum limits. Technological work by the European sugar producers showed that the levels of nitrite in feed materials from sugar plant processing is variable without allowing a stringent control at the full-scale factory process. The German Sugar Association (VdZ) reviewed the physiological-toxicological data base on nitrite in ruminants considered by EFSA (2009): The established toxicological endpoint of nitrite is oxidized hemoglobin (methemoglobin) that leads to a lack in oxygen supply. The review revealed that the NOAEL (No Observed Adverse Effect Level) of 3.3 mg nitrite/kg bw/day in ruminants is based on a 1940 study with 990 mg nitrate/kg bw in cattle in which nitrite is not mentioned. As auxiliary, a nitrite dose of 99 mg/kg bw was imputed, nitrite considered as being 10 times more toxic, and an uncertainty factor of 3 applied. Published physiological data, however, suggest that such a nitrate dose would be associated with a much higher nitrite exposure and support a lower toxicity of nitrite. To substantiate this assumption, cannulated cows received 7.5 mg nitrite/kg bw/day over a period of 7 days. After dosage, the expected transient increase of nitrite in ruminal fluid was observed that disappeared 1.5 h after dosage. No relevant increase in methemoglobin was observed. From this study, it can be concluded, that repeated feeding of 7.5 mg nitrite/kg bw to cows did not result in adverse effects. The dosage corresponded to 5.5 g nitrite intake per day and would cover the exposure from molasses with 500 mg nitrite/kg when the other feed contained 10 mg nitrite/kg. The data are supportive that nitrite is a normal metabolite in ruminants that does not require a regulation as contaminant in feed for ruminants.

Calcium Nitrate Dose and Application Period in American Lettuce (Lactuca sativa L.)

The aim of this study was to evaluate the yield of American lettuce subjected to different dosages of calcium nitrate on two application schedules. The experiment used four replicates of a 2 × 5 factorial randomized complete block design, with two application schedules (Schedule 1: 50% of the dose at transplanting and 50% at 20 days after transplanting; Schedule 2: 50% at 10 days and 50% at 20 days after transplanting) and five doses (0, 150, 300, 450 and 600 kg ha-1). The following variables were evaluated: the number of inner and outer leaves, head height and diameter, head height/diameter ratio, compactness, stem diameter, relative index of chlorophyll, commercial production and nitrogen (N) and calcium (Ca) content in the inner and outer leaf. The data were subjected to analysis of variance (F test, with Tukey test for comparison of the means) for the application schedule and regression analysis for the calcium nitrate dose. The application of calcium nitrate positively influenced the nutritional characteristics of American lettuce in the 2nd schedule and the dose of 470 kg ha-1 presented better production.

Nitrite: Review of existing and new physiological data in ruminants

Nitrite is regulated as an undesirable substance in animal feed. “Products and by-products from sugar beet and sugarcane” are currently exempted from maximum limits. Technological work by the European sugar producers showed that the levels of nitrite in feed materials from sugar plant processing is variable without allowing a stringent control at the full-scale factory process. The German Sugar Association (VdZ) reviewed the physiological-toxicological data base on nitrite in ruminants considered by EFSA (2009): The established toxicological endpoint of nitrite is oxidized hemoglobin (methemoglobin) that leads to a lack in oxygen supply. The review revealed that the NOAEL (No Observed Adverse Effect Level) of 3.3 mg nitrite/kg bw/day in ruminants is based on a 1940 study with 990 mg nitrate/kg bw in cattle in which nitrite is not mentioned. As auxiliary, a nitrite dose of 99 mg/kg bw was imputed, nitrite considered as being 10 times more toxic, and an uncertainty factor of 3 applied. Published physiological data, however, suggest that such a nitrate dose would be associated with a much higher nitrite exposure and support a lower toxicity of nitrite. To substantiate this assumption, cannulated cows received 7.5 mg nitrite/kg bw/day over a period of 7 days. After dosage, the expected transient increase of nitrite in ruminal fluid was observed that disappeared 1.5 h after dosage. No relevant increase in methemoglobin was observed. From this study, it can be concluded, that repeated feeding of 7.5 mg nitrite/kg bw to cows did not result in adverse effects. The dosage corresponded to 5.5 g nitrite intake per day and would cover the exposure from molasses with 500 mg nitrite/kg when the other feed contained 10 mg nitrite/kg. The data are supportive that nitrite is a normal metabolite in ruminants that does not require a regulation as contaminant in feed for ruminants.

Use of Acetate, Propionate, and Butyrate for Reduction of Nitrate and Sulfate and Methanogenesis in Microcosms and Bioreactors Simulating an Oil Reservoir

ABSTRACT Acetate, propionate, and butyrate (volatile fatty acids [VFA]) occur in oil field waters and are frequently used for microbial growth of oil field consortia. We determined the kinetics of use of these VFA components (3 mM each) by an anaerobic oil field consortium in microcosms containing 2 mM sulfate and 0, 4, 6, 8, or 13 mM nitrate. Nitrate was reduced first, with a preference for acetate and propionate. Sulfate reduction then proceeded with propionate (but not butyrate) as the electron donor, whereas the fermentation of butyrate (but not propionate) was associated with methanogenesis. Microbial community analyses indicated that Paracoccus and Thauera (Paracoccus-Thauera), Desulfobulbus, and Syntrophomonas-Methanobacterium were the dominant taxa whose members catalyzed these three processes. Most-probable-number assays showed the presence of up to 107/ml of propionate-oxidizing sulfate-reducing bacteria (SRB) in waters from the Medicine Hat Glauconitic C field. Bioreactors with the same concentrations of sulfate and VFA responded similarly to increasing concentrations of injected nitrate as observed in the microcosms: sulfide formation was prevented by adding approximately 80% of the nitrate dose needed to completely oxidize VFA to CO2 in both. Thus, this work has demonstrated that simple time-dependent observations of the use of acetate, propionate, and butyrate for nitrate reduction, sulfate reduction, and methanogenesis in microcosms are a good proxy for these processes in bioreactors, monitoring of which is more complex. IMPORTANCE Oil field volatile fatty acids acetate, propionate, and butyrate were specifically used for nitrate reduction, sulfate reduction, and methanogenic fermentation. Time-dependent analyses of microcosms served as a good proxy for these processes in a bioreactor, mimicking a sulfide-producing (souring) oil reservoir: 80% of the nitrate dose required to oxidize volatile fatty acids to CO2 was needed to prevent souring in both. Our data also suggest that propionate is a good substrate to enumerate oil field SRB.